MEXICO CITY – At least one U.S. citizen was among dozens of men reportedly forced off passenger buses by armed attackers in the northeastern border state of Tamaulipas, where 72 bodies were found in mass graves last week, U.S. officials said Sunday.

The man has yet to be located, said a warden’s message posted on the website of the consulate, which is located in the Tamaulipas city of Matamoros, across the border from Brownsville, Texas.

It is not unusual for people living or working in Mexican border states to have been born in the U.S.

In a separate warden’s message issued Friday, the consulate had warned that Mexican criminal gangs may be planning attacks “in the near future” against U.S. law enforcement or U.S. citizens in Tamaulipas, Nuevo Leon and San Luis Potosi, three northern states wracked by drug violence as cartels battle for territory.

The report said the information was uncorroborated but was being distributed to all U.S. employees in those three states. There was no mention of closing consulates or sending State Department workers out of the country.

A call by The Associated Press to the Matamoros consulate for more details wasn’t immediately answered.

The consulate’s statement did not say when or where the U.S. man went missing from the passenger bus.

“From late March to early April, the consulate received three reports from American citizens or their families regarding inter-city buses being boarded by criminals,” the warden’s message said.

“In at least one instance, male bus passengers, including an American citizen, were forcibly removed from those buses and have yet to be located.”

The consulate is warning U.S. citizens against traveling through Tamaulipas, either by public bus or private transportation.

Investigators uncovered the 72 bodies in 10 pits near San Fernando, a town about 90 miles (145 kilometers) south of Brownsville on a well-traveled stretch of highway that runs near the Gulf Coast. It is an area regularly patrolled by the Mexican military.

It was the second-such gruesome find in less than a year: In August, investigators found the bodies of 72 migrants in San Fernando.

Federal authorities said they are holding 14 people — 12 men and two women — as suspects in the latest case.

The federal Attorney General’s Office said there was evidence that most of the suspects belonged to the Zetas drug gang, the same group blamed for the August massacre. Some were detained with military-style uniforms, and others were found driving a pickup truck displaying false Mexican navy insignia.

The Zetas and rival Gulf Cartel are fighting in Tamaulipas over lucrative drug transit routes to the U.S. The state shares three major border cities with Laredo, McAllen and Brownsville, Texas.

Dozens of families and passengers complained of gunmen pulling people, mostly young men, off inter-city travel buses starting in late March, leading investigators to last week’s grisly discovery.

Investigators continued working over the weekend to find more graves and to identify the bodies.